1. Field of the Invention
The present invention relates to an improved apparatus and method for treating wood structures to arrest decay over extended periods of time. More particularly, the present invention relates to a method for packaging, dispensing, and safely introducing wood-protecting chemicals into the internal structure of wood.
2. Background of the Invention
Wood structures, particularly outdoor structures and supports, such as utility poles, piling supports, marine piles, and building components are subject to attack by wood-destroying fungi and insects. Often, such destruction can be ongoing and extensive internally before it is noticed externally.
One way to combat such destruction is to apply chemical(s) to the wood, preferably internally, which are toxic to these wood-destroying fungi and insects. Unfortunately, chemicals that are toxic to wood-destroying agents also are sometimes toxic to man, animals, plants, other insects, and to the environment, generally. Therefore, the release of such toxic agents into the wood structure must be carefully controlled and contained. Also, persons who are required to handle such chemicals may be in danger if they are not adequately protected during handling.
Effective protection of a wood structure will result only if the wood is treated over a long period of time; however, once a treatment is applied, it is nearly impossible to provide prolonged supervision of the treated structure. Therefore, the treatment should be inconspicuous so that children or animals do not tamper with the treatment, exposing themselves and others to potentially toxic chemicals.
Until recently, wood was treated with toxic chemicals by inserting enclosed packages of such chemicals into a preformed cavity in the wood. The chemicals were released by mechanical means, e.g., external mechanical pressure or for example, when the package contacted a puncturing device at the far end of the cavity. Another means for mechanically releasing such chemicals was to provide the chemicals in a cartridge which could be knocked into the wood using sufficient force to overpressure the cartridge and cause the chemicals to be injected into the wood. The shattering technique added the risk that shattered pieces of the cartridge might harm the person who was applying the cartridge, or otherwise harm the surrounding environment and its inhabitants.
One method used to minimize the foregoing risks was to use a container which permits a time-delayed release of the chemicals. Typically, time-delayed release involves the use of a container with at least a portion that will dissolve after a period of time. For example, a container may have a plug that is impermeable to the chemicals in the container, but chemically reactive so that the plug dissolves after a period of time. Alternately, the chemicals can be in a permeable package inside of an impermeable but chemically reactive outer container which dissolves after a period of time.
Time-delayed application of wood-treatment chemicals is safer than previous methods. Unfortunately, time-delayed application typically has a relatively short duration because, once the chemically reactive portion of the fumigant container dissolves, the release of the chemicals is substantially uncontrolled. As a result, the chemicals tend to dissipate more rapidly than desired.
U.S. patents of interest include, for example, Fahlstrom, U.S. Pat. No. 4,344,250; Hobbs, U.S. Pat. No. 5,244,615; Blom, et al., U.S. Pat. No. 4,389,446; Hollister, U.S. Pat. No. 1,999,458; Imus, U.S. Pat. No. 2,923,039; Loft, et al., U.S. Pat. No. 3,745,057; Errede, et al., U.S. Pat. No. 4,207,705, Baker, et al., U.S. Pat. No. 4,445,641; Amick, U.S. Pat. No. 4,552,752; Allan, et al., U.S. Pat. No. 4,554,155; Frimel, et al., U.S. Pat. No. 4,597,218; Drake, U.S. Pat. No. 4,793,474; and Frimel, et al., U.S. Pat. No. 4,932,155.
Other patents of interest include, House, Japan 4070972, filed Jun. 7, 1979; Shemelsu, Japan 7050901, filed Mar. 25, 1982; Heinen, Great Britain 848,122, filed Sep. 14, 1960; Freyberg, European Patent 131,759, filed Jan. 23, 1985; and Ghys, Australia 221,947, filed Jul. 27, 1958.
All references, articles, patents, patent applications, standards, and the like cited herein are incorporated by reference in their entirety.
A safe method to prevent wood decay using the long-term controlled release of wood-treating chemicals would be highly desirable. The present invention provides such a method.
The present invention provides an apparatus and method for controlled release of a fumigant into a wood structure to prevent decay of that structure. According to the present invention, a fumigant in a sealed polymer ampule or container is inserted into the wooden structure. The ampule or container is made of a polymeric organic material that does not react with the fumigant, but is permeable to the fumigant such that, when inserted into the wooden structure, the rate of release of the fumigant through the ampule wall is slow enough to continuously treat and arrest decay of the wooden structure, particularly decay caused by fungi, over extended periods of time (i.e., 1 to 30 years). The rate of release of a fumigant or mixture of fumigants can be controlled by the shape of the container, the nature of the polymer used to make the container, and by the thickness of the container wall.
In another aspect, the present invention relates to a wooden structure protected from decay for a prolonged period of time, comprising:
a wooden structure; and
a fumigant in at least one sealed container inserted into said wooden structure, which container has walls comprising a fiber-free heat sealable organic polymer ampule, which is a multiple layer or single layer tube sealed or closed at one or both ends that is permeable to but otherwise inert to said fumigant, the walls allowing the fumigant to be retained while permitting controlled release of a sufficient amount of the fumigant to diffuse at a rate of fumigant loss of between about 1 and 15 mg/day through said walls to protect said wooden structure from decay for a period of time of up to at least 7 years or for up to about 30 years, with the proviso that no external force other than ambient pressure and temperature is present to release the fumigant from said sealed container. Preferably, the polymer comprises a chemically modified or non-modified thermoplastic polymer.
Preferably, in the protection of the wood structure the polymer is selected from the group consisting of a high density polyethylene polymer, a polypropylene polymer, a crosslinked polyethylene, a crosslinked polypropylene, a surface fluorinated high-density polyethylene polymer, a fluoroalkoxyfluorocarbon polymer, and a polyvinylidene fluoride polymer resin. The walls of the polymer container are usually between about 5 and 100 mils thick, preferably between about 5 and 50 mils thick, and more preferably between about 5 and 25 mils. In some specific applications, the walls of the polymer container are between about 8-12 mils thick.
In another aspect, the invention relates to a method for long-term protection of a wooden structure from decay comprising:
inserting a fumigant in a sealed container into said wooden structure, said container having walls comprising a fiber-free, heat-sealable organic polymer ampule, which is a single layer tube sealed at both ends that is permeable to but otherwise inert to the fumigant, said walls allowing the fumigant to be retained while permitting controlled release of a sufficient amount of said fumigant to diffuse at a rate of fumigant loss of between about 1 and 15 mg/day through the walls to protect the wooden structure from decay for a period of time of between about 2 to 30 years or up to at least 7 years or for up to about 30 years, with the proviso that no external force, other than ambient pressure and temperature, is present to release said fumigant from the sealed container.
In another aspect, the present invention concerns a wooden structure treated by a process, which process comprises:
inserting a fumigant in, at least one sealed container into said wooden structure, the container having walls comprising a fiber-free, heat-sealable organic polymer ampule, which is a single or multiple layer tube sealed at both ends that is permeable to but otherwise inert to said fumigant, the walls having a thickness sufficient to retain the fumigant while permitting controlled release of a sufficient amount of the fumigant to diffuse at a rate of fumigant loss of between about 1 and 15 mg/day through the walls to protect said wooden structure from decay for a period of time of up to at least 1 year or for up to about 30 years, with the proviso that no external force other than ambient pressure and temperature is present to release the fumigant from the sealed container.
Preferably, the wooden structure is protected using a polymer selected from the group consisting of a high density polyethylene polymer, a polypropylene polymer, a crosslinked polyethylene polymer, a crosslinked polypropylene polymer, a surface fluorinated high-density polyethylene polymer, a fluoroalkoxyfluorocarbon polymer, and a polyvinylidene fluoride polymer resin; and the fumigant is selected from the group consisting of chloropicrin, methyl isothiocyanate, and sodium N-methyl-dithiocarbamate.
Preferably the polymer is selected from the group consisting of fluorocarbons, and (surface fluorinated) polyolefins.
Preferably the polymer is a surface fluorine modified high density polyethylene polymer having a wall thickness of between about 8 to 12 mils;
the fumigant is chloropicrin; and the time of release is up to about 7 years.
In a preferred aspect, the fumigant is selected from the group consisting of chloropicrin, methyl isothiocyanate and sodium N-methyl-dithiocarbamate;
the polymer of the container is selected from the group consisting of a surface fluorinated high-density polyethylene polymer, a fluoro-alkoxyfluorocarbon polymer, and a polyvinylidine fluoride resin; and
the prolonged time is up to at least about 1 year or up to about 7 years or up to about 30 years.
In a specific aspect, the present invention relates to a method for long-term protection of a wooden structure from decay comprising:
inserting a fumigant in a sealed container into the wooden structure, the container having walls of an organic polymer ampule, which is a fiber free, heat sealable single layer tube which is sealed at both ends, that is permeable to but otherwise inert to the fumigant, the walls allowing the fumigant to be retained while permitting controlled release of a sufficient amount of the fumigant to diffuse at a rate of fumigant loss of between 1 and 15 mg/day through the walls to protect the wooden structure from decay for a prolonged period of time, which prolonged time is obtained by selection of a polymer container and a weight of fumigant, with the proviso that no external force, other than ambient pressure and temperature, is present to release said fumigant from the container.